#### Answer

Mass % of Na = 32.37%
Mass % of S = 22.575%
Mass % of O = 45.055%

#### Work Step by Step

Mass percentage of an element =
(mass of that element in the compound × 100)/(molar mass of the compound)
Molar mass of sodium sulfate ($Na_{2}SO_{4}$)= $(2\times22.99g)+(1\times32.065g)+(4\times15.999g)$ = 142.04g
Mass % of Na = $\frac{(2\times22.99g)\times100}{142.04g}$ = 32.37%
Mass % of S = $\frac{32.065g\times100}{142.04g}$ = 22.575%
Mass % of O = $\frac{(4\times15.999g)\times100}{142.04g}$ =45.055%